He was wearing a protective when he had the reoccurance of the stress fracture. Since the last time he played then went missing again and people were speculating he'd done it again we saw his legs visible in the video where he signed a new deal and we saw him training in Dubai pictured with Matip and Thiago (maybe other players being eased back in) albeit in trainers not football boots.
I doubt it's the stress fracture again.
Not sure that your doubt is warranted. In the absence of other information, and on balance of probabilities, it's comfortably the most likely option.
Don't see how current absence of boot means much. How long was he wearing the boot initially and after the reinjury?
His last game was 6 November (almost 6 weeks ago). It was around 6 weeks after his first injury that he came back to full training (briefly, before reinjury). For him to be doing light training in trainers seems entirely in line with timescales of the previous two occurrences.
BTW you've contradicted yourself on the contract signing video. Haven't seen it, but at the time you said that it didn't show his feet (you used that to make a cheap dig that I was a conspiracy theorist for saying it was likely he was injured again). Now suddenly you say you could see his feet.